The goal of the research is an understanding of the basic neurochemical processes by which hormones affect behavior. Sexual behavior in the female rat is a convenient model, because the behavior is completely dependent on estrogen and progesterone, and previous work has established that an important site of these actions is the ventromedial hypothalamus. The most likely mechanism by which estrogen progesterone affect the behavior is a change in protein synthesis elicited by steroid receptors in cell nuclei. However, little is known about proteins that might be modified by either hormone, and alternative hypotheses have been proposed for progesterone's effects. the proposed experiments will directly test the hypothesis that progesterone modifies protein synthesis in the ventromedial hypothalamus of the female rat. labeled amino acid precursors will be infused into the ventromedial hypothalamus of ovariectomized rats. The patterns of proteins synthesized after control injections, estradiol alone, or estradiol plus progesterone will be analyzed using tow dimensional gel electrophoresis. The hypothesis predicts that there will be three different patterns of protein synthesis in rats which receive the different treatments. it is further hypothesized that some hormonally modified proteins will be transported to the midbrain central gray, and area known to be an important link in inducing sexual receptivity. The time course of progesterone's effect on protein synthesis will be investigated, and the ability of a progestin receptor antagonist to block the protein synthesis changes will assessed. Finding that progesterone modifies the synthesis of specific proteins in the brain would open a new avenue for studies of mechanisms by which hormones affect behavior.